There is a growing need for windows or other visually transparent openings in buildings that block against electromagnetic and infrared radiation in order to prevent the undesired collection of data from computer devices in the buildings. The level of blocking of electromagnetic and infrared radiation to provide the desired anti-surveillance security can vary over a wide range depending on the different security requirements. For the highest level of blocking, such as blocking of greater than 99% of the electromagnetic and infrared radiation, one challenge is to maintain an acceptable and as high as possible a transmission of visible light so that the normal function of the window for clarity and haze-free viewing is still provided. Another challenge is to readily obtain grounding of the electromagnetic blocking layers in the security window in order to achieve good electrical attenuation over a wide range of frequencies.
Since the 1990's, conductive glass windows from Pilkington have been sold under the trade name of DATASTOP for shielding against electromagnetic radiation in both laminated glass and insulating glass units. These conductive glass windows provide electromagnetic shielding for all but the most demanding data security applications, but do not provide sufficient infrared shielding for most anti-surveillance applications.
U.S. Pat. Nos. 6,859,310, 6,891,667, 7,177,075, 7,295,368 and 7,405,872 describe various approaches to designing security windows using a highly electrically conductive filter layer of a plurality of dielectric and metal layers with an infrared transmission at wavelengths between 780 nm and 2500 nm of no more than 50% and a sheet resistance of less than 4 ohms per square.
It would be advantageous to have a security window design that provides a combination of ease of grounding, electromagnetic and infrared shielding for the most demanding anti-surveillance applications, and high visible light transmittance and clarity.